Aromatic hydrogenation

ABSTRACT

A process for the low pressure hydrogenation of aromatic hydrocarbons in the presence of sulfur employing a fluorided platinum-alumina catalyst and carbon monoxide as a conversion reaction moderator. By employing a fluorided platinum-alumina catalyst and the moderator carbon monoxide, aromatic hydrocarbon saturation is accomplished while simultaneously inhibiting concurrent hydrocracking reactions.

United States Patent 1' Estes vet al.

[ 1 Jan. 16, 1973 [54.1 AROMATIC HYDROGENATION [75] Inventors: John H. Estes, Wappingers Falls; Sheldon Herbstman, Spring Valley; Stanley Kravitz, Wiccopee, all of NY.

[73] Assignee: Texaco Inc., New York, NY.

[22] Filed: Nov. 25, 1970 [21] Appl. No.: 92,894

[52] US. Cl ..260/667, 208/143 1 [58] Field ofSearch ..260/667; 208/143 [56] References Cited UNITED STATES PATENTS 3,531,396 9/l970 Messing et al. ..260/667 UX 3,435,085 3/l969 White et al. ..260/667 3,285,984 l 1/1966 Goble' ..260/667 2,757;l28 7/l956 Hemminger ..260/667 Primary Examiner-lames E. Poer Assistant ExaminerP. F. Shaver Attorney-Thomas H. Whaley and Carl G. Reis [57] ABSTRACT ;moderator carbon monoxide, aromatic hydrocarbon saturation is accomplished while simultaneously inhibiting concurrent hydrocracking reactions.

11 Claims, N0 Drawings AROMATIC HYDROGENATION BACKGROUND OF THE INVENTION This invention relates to a process for the catalytic hydrogenation of aromatic hydrocarbons. In particular, this invention relates to a process for hydrogenating aromatic hydrocarbon feedstocks containing sulfur contaminants to produce naphthenic hydrocarbons.

Processes for the hydrogenation of aromatic hydrocarbons and aromatic feedstocks containing sulfur have previously been studied. To hydrogenate such hydrocarbons, the art has suggested two-step processes consisting of initial desulfurization in the presence of a first catalyst such as cobalt-molybdenum on alumina followed by hydrogenation over a platinum metal catalyst. 1n the absence of initial desulfurization, sulfur contaminants such as naturally occurring organo sulfur compounds cause rapid deactivation of the platinum catalyst. More recently, the art has been taught that certain highly fluorided platinum-alumina catalysts retain some resistance to sulfur poisoning such that initial desulfurization of the feedstock may be eliminated. While these fluorided platinum-alumina catalysts successfully hydrogenate aromatic feedstocks in the presence of sulfur, an undesirable amount of hydrocracking concurrently occurs by virtue of the highly acidic nature of the catalyst. Moreover, to accomplish a high degree of hydrogenation of aromatic hydrocarbons containing substantial amounts of sulfur, fluorine contents of at least weight percent were taught and the reaction itself was preferably conducted at elevated pressures of 1,000 to 4,000 p.s.i.a.

[t is therefore, an object of this invention to provide a process for the hydrogenation of aromatic hydrocarbon s in the presence of sulfur at low pressures.

Another object of this invention is to provide a process for the hydrogenation of aromatic hydrocarbon feedstocks containing sulfur in the presence of a sulfur resistant catalyst while simultaneously inhibiting undesirable hydrocracking reactions.

Yet another object of this invention is to provide a single stage low pressure hydrogenation process for hydrogenating aromatic hydrocarbons in the presence of sulfur which obviates the need for a prior desulfurization step.

Other objects and advantages will become apparent from a reading of the following description and examples.

SUMMARY OF THE INVENTION Broadly, this invention contemplates a process for the hydrogenation of aromatic hydrocarbons in the presence of sulfur which comprises contacting said aromatic hydrocarbon in the presence of sulfur with hydrogen and a fluorided platinum-alumina catalyst in the presence of carbon monoxide.

In accordance with the present invention, it has now been discovered that introduction of small amounts of carbon monoxide during the hydrogenation reaction inhibits the cracking propensity of the highly active fluorided platinized-alumina catalyst. Beneficial effects provided to the reaction by carbon monoxide addition was unexpected inasmuch as carbon monoxide has long been considered a strong general poison toward platinum metal catalysts. Notwithstanding its heretofore known deleterious effects, the introduction of small amounts of carbon monoxide in the course of hydrogenating aromatic hydrocarbons provides a means for controlling the reaction selectivity.

Pursuant to this invention, hydrogenation of aromatic hydrocarbons is undertaken at conditions including temperatures of from 400 to 750F., preferably from 550F. to 725F., at liquid hourly space velocities of from 0.2 to 5 v/v/hr, preferably from 0.5 to 2.0 LHSV, at hydrogen to hydrocarbon mole ratios in the range of about 5:1 to 1:1 and hydrogen gas feed rates of from 2,000 to 10,000 standard cubic feet per barrel and preferably from 2,000 to 5,000 SCF/bbl. Significantly, the instant process can be successfully conducted at low pressures, i.e., from 300 to 1,000 p.s.i.g. and preferably from 300 to 500 p.s.i.g., thereby permitting the reaction to be undertaken within conventional conversion equipment and alleviating the high investment associated with high pressure reactors and equipment.

The catalyst employed in our process consists essentially of a fluorided platinum-alumina catalyst wherein the fluorine content ranges from about 0.5 to 15.0 weight percent based on the total weight of catalyst. Platinum is present in an amount of from 0.1 to 10.0 weight percent and preferably 0.5 to 2.0 weight percent. Aluminas in various forms may be used in this invention and particularly those aluminas having replaceable surface hydroxyl groups and surface areas of from 50 to 800 square meters per gram using the BET method. Included within our definition of alumina, we mention for example eta-alumina, gammaalumina, silica stabilized-alumina, i.e., aluminas containing approximately 5 weight percent silica, thoriaalumina, zirconia-alumina and titania-alumina. Preferably, we employ aluminas having surface areas of from 50 to 400 square meters per gram and particularly etaand gamma-alumina.

The catalyst described above can be prepared by methods known to the art. Platinum, as a component of the catalyst, can be provided to the alumina by impregnating with a soluble platinum salt followed by calcination at temperatures of from 600 to 1,200F. for several hours. Additional acidity is introduced to the platinum-alumina composite by contacting the composite with a fluoriding agent such as aqueous hydrogen fluoride, vaporized boron or ammonium fluoride or treatment with other well known fluoriding compounds such as carbon tetrafluoride or sulfur tetrafluoride thereby introducing to the catalyst chemically combined fluorine in an amount of from 0.5 to 15.0 percent and preferably from 0.5 to 5.0 weight percent fluorine.

We believe that the role of carbon monoxide in our process for the hydrogenation of the feedstock containing an aromatic hydrocarbon in contact with the above mentioned catalyst is to inhibit the cracking activity of the catalyst, while simultaneously permitting its hydrogenation activity to function, i.e., to say to interfere with the acidity function of the catalyst surface while at the same time avoiding permanent damage or poisoning of the catalyst surface. In this regard we have found that low concentrations of carbon monoxide introduced in the course of the hydrogenation process strongly modifies the product distribution such that the catalyst is moderated to the extent that the cracking propensity of the catalytic material is inhibited. Illustratively, the course of aromatic conversion in the presence of the fluorided platinum-alumina catalyst is modified from that of permitting a plurality of reactions, including hydrocracking, to take place to one predominantly of hydrogenation. Conversely, discontinuation of carbon monoxide introduction to the process results in reversal of catalyst selectivity and returns the reaction to the original conditions, i.e., to say substantial hydrocracking of the feedstock will occur.

Extremely low concentrations of carbon monoxide introduced in the course of hydrogenating the aromatic hydrocarbon have been found to perform the function detailed above. The amount of carbon monoxide beneficially employed and introduced in the course of the process varies from about 2.5)(10' to 1.0 l'

gram mole of carbon monoxide per hour per gram of the fluoride platinum-alumina catalyst and preferably from 5XlO"-" to IXlO" gram mole of carbon monoxide per hour per gram of said catalyst. In selecting the amount of carbon monoxide introduced to particular reactions we have found that the rate of carbon monoxide introduction is dependent upon the temperature of the reaction such that the higher amounts of carbon monoxide are required to inhibit hydrocracking at the higher temperatures while lesser amounts perform the same function at lower temperatures. That is, amounts such as 5X10 to 1.0Xl0' gram mole of carbon monoxide per hour per gram of catalyst are sufficient where the process is carriedout at temperatures of about 650F. whereas higher amounts such as 1X10" to IXIO'" are needed when processing temperatures are about 750F. Likewise, carbon monoxide introduction and its affect upon the process is responsive to the percent fluorine on the catalyst. A catalyst containing lower amountsof fluorine such as 0.5 weight percent requires less carbon monoxide to moderate the reaction whereas fluorine contents of about weight percent require the higher rates of carbon monoxide introduction. One convenient means of introducing carbonmonoxide to the reaction zone has been to add carbon monoxide to the hydrogen stream prior to hydrogen introduction to the reaction chamber. Carbon monoxide introduction can be on a continuous basis or, alternatively, carbon monoxide may be pulsed or intermittently introduced to the reaction such that the rate of carbon monoxide introduction is within 2.5% 10 mm 103(11) gram mole per hour per gram of catalyst.

By providing a means for moderating catalyst activity and selectivity in the process recited above through the use of carbon monoxide, aromatic hydrocarbons such as benzene, alkylbenzenes, naphthalene and alkylnaphthalenes are readily hydrogenated. The instant process is admirably suited for hydrogenating such sulfur containing aromatic feed stocks as niarginal kerosenes and upgrading the same to jet fuel quality. By marginal kerosenes, we mean materials which distill in the kerosene range but which do not meet specifications with respect to smoke point or other properties required for AVJET-A. Typically, sulfur containing marginal kerosenes can be hydrogenated according to our process such that their product quality can be upgraded to an acceptable or exceptional level insofar as meeting recog nized specifications for use in military and civilian aviation is concerned. lllustratively, marginal kerosenes heavy in aromatics as for example above 15 volume percent and particularly above 26 volume percent can be hydrogenated such that the aromatics content is reduced to at least below l5 volume percent as determined by Fluorescent lndicator Analysis (FlA) ASTM D-l3l9. Likewise initial sulfur concentrations of 290 to 1500 ppm can be reduced to ppm and lower. Smoke points as determined by ASTM No. D-l322 of marginal kerosenes are likewise improved from levels of about 15 mm to desirable levels of 2| to 30 mm. Any olefins present in the feed are saturated and the sulfur contaminants are converted to hydrogen sulfide, the latter being separated and recovered by scrubbing with monoethanolamine and dior triethylene glycol.

In addition to upgrading marginal kerosenes, our process provides a means for converting other heavy aromatics from such sources as gas oil hydrocracking by hydrogenation to alkylnaphthenes suited for use as high performance jet fuels. Aromatics are also readily available from such refinery streams as the bottoms from a catalytic reforming unit or as cycle oil from catalytic cracking and are generally of the bicycle type which are hydrogenated by our process to the corresponding naphthene. Hydrogenation of the aforementioned aromatic hydrocarbons best meet the volatility and freezing point requirements of the high performance jet fuels having initial boiling points of about 310F. and end points of 550F.

In order to more fully illustrate the nature of our invention and manner of practicing the same the following examples are presented. I

EXAMPLE I A feedstock of marginal value as an aviation jet fuel described in Table 1 containing aromatic hydrocarbons and sulfur was introduced to hydrogenation reactors containing 57.0 grams each of catalysts identified as A and B, where catalyst A was 0.5 weight percent platinum on alumina and catalyst B was fluorided platinum on alumina having a platinum content of 0.5 weight percent and a fluorine content of 4 weight percent. The feedstock was hydrogenated at low pressure in the presence of each catalyst in Runs l-6 under the conditions summarized in Table l.

TABLE I Run number Feedstock 1 2 3 4 5 6 Catalyst A B B B B B Conditions Temperature, F. 650 650 650 650 650 650 H pressure p.s.i.g 500 500 500 500 800 800 H, rate, s.c.f./bbl 2, 400 2, 400 4, 800 4, 800 4,800 4, 800 LHSV 1.0 1.0 1.0 1.0 1.0 1. 0 00 gm. molelhnlgm. catalyst 2 5X10- i. 5x10-4 Time, hrs 48 30 60 4B 48 Liquid yiold, vol. percent 95.8 104. 3 101. 2 99. 7 98. 6 O8. 2 Hz consumption, s.c.t lbbl 1, 084 894 Run number Feedstock 1 2 8 4 5 Product. quality:

Armnntics, vol. pcrconl. (FlA). 10.0 15. 5.0 2.0 5.0 l. 0 h'uioko point, mm. N 1'. 20 25. 6 30. 0 2B. 3 32. 0 28. 2 (lruvity, All 41. 4 42. 4 51. 7 65. 48. 7 41!. 40. 4 Sulfur, p.p.m. L90 20-00 10 10 ASTM distillation, l

111 1 330 326 96 134 128 114 6 vol. percent 350 355 173 266 141 314 10 vol. percent. 365 368 228 311 255 338 vol. percent. 371 380 295 263 346 295 360 vol. percent 403 330 302 362 334 373 50 V01. percent. 415 412 374 353 388 376 398 70 vol. percent- 445 435 403 391 412 410 421 90 vol. percenL 482 470 455 448 448 447 457 E P 608 517 494 469 489 494 498 1 None APl gravity was determined employing ASTM D- We claim:

From Table i it will be seen that processing of the. feedstock in the presence of catalyst A at a low;

hydrogen pressure and under the conditions described in Run No. 1 resulted in essentially no hydrogenation basis the values on aromatics content, smoke point and distillation range. The subsequent Runs 2-6 all employed a fluorided platinum-alumina catalyst. Comparing Runs Nos. 1 and 2, No. 2 resulted in a reduction in aromatics content and an increase in smoke point. However, considerable hydrocracking occurred and is reflected in the high APl gravity of 51.7 and in the distillation range of the product where 30 volume percent of the product distills below 3l0F., 310F. being the initial boiling point requirement for aviation jet fuels. Run No. 3 is similar to Run No. 2 except that a higher rate of hydrogen introduction was employed resulting in a higher APl gravity and between 30 to 50 volume percent of the product distilling below 310F. In Run No. 4 the conditions employed in Run No. 3 were repeated except that carbon monoxide was introduced in the course of hydrogenation. From the results of Run No. 4 the benefits of the present invention are shown in that carbon monoxide introduction has not impaired the catalysts ability to saturate aromatics, nor interferred with the function of increasing the smoke point of the treated feedstock. Significantly, (1) the Aliigravity of the produ t was lower (48.7) when carbon monoxide was present during processing, (2) the distillation range shows that less than 10 volume percent of the product distills below 310F. and (3) hydrogen consumption was reduced from 1,084 to 894 SCF/bbL, all indicating that undesirable hydrocracking was successfully inhibited. Runs 5 and 6 conducted at hydrogen pressures of 800 p.s.i.g. respectively in the absence and presence of carbon monoxide provide similar results and illustrate the benefits of this invention.

1. A process for the hydrogenation of aromatic hydrocarbons in the presence of sulfur which comprises contacting said hydrocarbon with hydrogen and a fluorided platinum-alumina catalyst in the presence of carbon monoxide.

2. A process according to claim 1 wherein said contacting is conducted at a hydrogen pressure of from 300 to 1,000 p.s.i.g.

3. A process according to claim 1 wherein said contacting is conducted at a hydrogen pressure of from 300 to 500 p.s.i.g.

4. A process according to claim 1 wherein said contacting is conducted at a temperature of from 400 to 750F.

5. A process according to claim 1 wherein said contacting is conducted at a temperature of from 550 to 725F.

6. A process according to claim 1 wherein said carbon monoxide is introduced at the rate of from about 2.5X 10* to 10X 10' gram mole of carbon monoxide per hour per gram of said catalyst.

7. A process according to claim 1 wherein said carbon monoxide is introduced at the rate of from about 5 l0'to 1X10" gram mole of carbon monoxide per hour per gram of said catalyst.

8. A process according to claim 1 wherein said contacting is conducted at a liquid hourly space velocity of from 0.2 to 5.0.

9. A process according to claim 1 wherein said contacting is conducted at a liquid hourly space velocity of from 0.5 to 2.0.

10. A process according to claim 1 wherein said hydrocarbon is a marginal kerosene fraction having an aromatic content of more than 15 volume percent.

11. A process according to claim 1 wherein said catalyst comprises from 0.1 to 10.0 weight percent platinum and 0.5 to 15.0 weight percent fluorine. 

2. A process according to claim 1 wherein said contacting is conducted at a hydrogen pressure of from 300 to 1,000 p.s.i.g.
 3. A process according to claim 1 wherein said contacting is conducted at a hydrogen pressure of from 300 to 500 p.s.i.g.
 4. A process according to claim 1 wherein said contacting is conducted at a temperature of from 400 to 750*F.
 5. A process according to claim 1 wherein said contacting is conducted at a temperature of from 550 to 725*F.
 6. A process according to claim 1 wherein said carbon monoxide is introduced at the rate of from about 2.5 X 10 5 to 10 X 10 3 gram mole of carbon monoxide per hour per gram of said catalyst.
 7. A process according to claim 1 wherein said carbon monoxide is introduced at the rate of from about 5 X 10 5 to 1 X 10 4 gram mole of carbon monoxide per hour per gram of said catalyst.
 8. A process according to claim 1 wherein said contacting is conducted at a liquid hourly space velocity of from 0.2 to 5.0.
 9. A process according to claim 1 wherein said contacting is conducted at a liquid hourly space velocity of from 0.5 to 2.0.
 10. A process according to claim 1 wherein said hydrocarbon is a marginal kerosene fraction having an aromatic content of more than 15 volume percent.
 11. A process according to claim 1 wherein said catalyst comprises from 0.1 to 10.0 weight percent platinum and 0.5 to 15.0 weight percent fluorine. 